Synthetic investigations of rapamycin. 2. Synthesis of a C(22)-C(42) fragment
摘要:
A concise, modular synthesis of a protected C22-C42 segment of rapamycin is reported including as key coupling steps a vinyllithium addition to a Weinreb amide (5 + 6 --> 24) and a nucleophilic epoxide opening with an alpha-lithio sulfone mediated by BF3.OEt2 (4 + 27 --> 28).
1,5-Stereocontrol in Bismuth-Mediated Reactions between Aldehydes and Allyl Bromides: Stereoselective Synthesis of Open-Chain all-syn- and anti, anti-1,3,5-Disposed Trimethylalkanes
作者:Eric Thomas、Norazah Bazar、Sam Donnelly、Hao Liu
DOI:10.1055/s-0029-1219357
日期:2010.3
The reaction of 5-benzyloxy-2,4-dimethylpent-2-enyl bromide with the bismuth species generated by reduction of bismuth(III) iodide by zinc powder gives an intermediate which reacts with aldehydes with useful levels of stereocontrol in favour of 1,5-anti-(3E)-5-methylalk-3-enols. Manipulation of protecting groups, stereoselective hydrogenation, and tosylate displacement using a higher-order cyanomethylcuprate